Keel Cooled Refrigeration in Freshwater Tanks?

[GordMay]

Originally Posted by a64pilot

... 1 Person apparently radiates 100W of heat on average ...

The Average Metabolic rate for an adult male (females and children average less) varies between about 100 watts and 430 watts, depending upon activity level.
1 W = 3.41 Btu/hr
ie:
Seated at rest = 100 W
Light bench work = 220 W
Heavy work = 430 W

[poiu]

I think the best solution I saw was on Dashew's website. He uses a small isolated compartment of his water tank into which he fits a keel cooler. The water tank disperses heat through the hull and because it is separate can be kept full always. There is no hole in the hull and no fouling or drag losses or galvanic corrosion worries or requirement to replace zincs. So he gets the full benefit of the lowest possible energy use refrigeration, no fan noise and puts most of the refrigeration heat out of the boat.

Modern keel cooler units have factory fitted filters now and I don't think they will block the system like they used too. My two 15 year old units have never failed for what it is worth.

[Terra Nova]

Dashew's boats are aluminum, one of the best heat sinks.

[poiu]

Originally Posted by Terra Nova

Dashew's boats are aluminum, one of the best heat sinks.

Indeed, but solid fibreglass should let plenty of heat out too. It will require a bigger surface area than an aluminium tank to do the same job.

[Terra Nova]

Fiberglass is an insulator. Aluminum is a heat sink.

[poiu]

Originally Posted by Terra Nova

Fiberglass is an insulator. Aluminum is a heat sink.

Fibreglass might be an insulator, but I would't describe GRP as an insulator. GRP boats in cold climates are not at all warm. Whilst it is also it is true that GRP is not remotely comparable to aluminium in its heat conductivity capability it is still capable of heat conduction. The conductivity values are 205 W /m K for aluminium, 0.23 for GRP (and .04 for fibreglass insulation).

Anyway, using the above value for GRP shows that a 1m2 area of 25mm thick fibreglass with a 7deg C temperature difference is capable of conducting 64 W of heat. A bit more than what you need for two BD50 compressors running at a 50% duty cycle. (.23 X 7/.025). Looks workable to me.